Cannot create a disk partition image on a mounted external usb hard drive

[Steve Singer]

Package:
gnome-disk-utility-3.10.0_1ubuntu3_i386

OS:
LiveDVD Ubuntu 14.04.1 ubuntu 3.13.0-32 i686

Hardware:
Dell Dimension 4550 4mB Pentium 4
Seagate Backup Plus 1TB

I tried to create a disk image of the primary disk's boot partition on an external USB backup drive.

From a terminal window:

ubuntu@ubuntu:~$ gnome-disks
   or
ubuntu@ubuntu:~$ sudo gnome-disks

The partition to be imaged was not mounted.
The permissions for the destination directory were 'drwxrwxrwxt' [1777]

When I tried to create the image, the error message:

   "Error allocating space for disk image file: Invalid argument (g-io-error-quark, 13)"

appeared.

In the terminal window from which gnome-disks was invoked, there was a repeating error message until the error dialog was dismissed:

   "(gnome-disks:6765): GLib-GIO-CRITICAL **: g_dbus_interface_get_object:
     assertion 'G_IS_DBUS_INTERFACE (interface_)' failed"